Mosquito spraying mission ends abruptly

The pilot was performing mosquito control spraying operations at 100 feet above ground level (agl) in Mobile, Alabama, when the rear engine of the Cessna 336 began to sputter and lose power.

He switched to the auxiliary fuel tank, however this did not remedy the situation.

He then climbed to 500 feet agl and continued to troubleshoot the problem by again switching fuel tanks and turning the electric boost pumps on.

Soon after, the front engine began to lose power. Unable to regain full power on both engines, he chose to perform a forced landing in an open field.

The airplane touched down on soft soil and stopped abruptly, which resulted in extensive damage to the plane and serious injuries to the pilot.

Both fuel selectors were found in the right main fuel tank positions. An examination of the fuel system revealed that the main fuel tanks contained only residual fuel and that the auxiliary tanks contained an adequate amount of fuel.

Examination of the fuel lines revealed that both supply lines from the gascolators to the engine-driven fuel pumps were contaminated and obstructed with a granular, powder-like substance.

The engines ran normally when operated in a test cell after the accident.

The auxiliary fuel tanks were designed for level, cruise flight only. The auxiliary tanks fed directly to the fuel selector and had no boost pumps available. It is likely that, due to the fuel system’s design, adequate fuel pressure could not be regained once the main tanks were depleted and the pilot switched to the auxiliary tanks.

The contamination in the fuel lines might have further restricted fuel flow to the engines.

The loss of engine power might have been prevented if the pilot had maintained an adequate amount of fuel in the main tanks.

The NTSB determined the probable cause as the pilot’s inadequate preflight fuel planning during which he did not ensure that there was adequate fuel in the main tanks for the flight, which resulted in a loss of engine power.